The back half of "Arrow" Season 5 will see the introduction of Talia al Ghul, and executive producer Wendy Mericle promises that she'll be a big piece of the Prometheus puzzle. Speaking to TVLine, Mericle revealed that Talia plays a “crucial part” in the mystery behind Prometheus.

"Arrow" won't be Talia's first "Arrow"-verse debut. After all, she appeared on "DC's Legends of Tomorrow," albeit as a child. The time travelling team met Talia in the '50s, after Sara, Ray Palmer and Kendra Saunders were stranded there by the Waverider for two years. However, "Arrow's" Talia will be a full grown adult played by "The 4400's" Lexa Doig.

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Debuting in the "Arrow" winter premiere, Talia is the latest member of the al Ghul family to appear on the CW show; her half-sister Nyssa al Ghul (Katrina Law) played a major part in “Arrow” seasons two through four, and their father Ra’s al Ghul (Matt Nable) was a major villain in season three of the show. The better-known daughter of Ra’s al Ghul, Talia al Ghul debuted in “Detective Comics” #411 in 1971. She initially served as a love interest for Batman, with most of her villainous acts coming at the request of her father Ra’s al Ghul. She’s been trained by the League of Assassins and is a deadly hand-to-hand combatant and is also skilled in the use of numerous weapons. More recently, Talia has become an adversary of Batman in her own right.

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Mericle also weighed in on the big Laurel Lance mystery, saying that her reappearance “is a very welcome surprise... But there will be… whatever the reverse of a ‘silver lining’ is… when [Oliver] finds out what’s really going on. It will have a lot of emotional resonance, particularly for him and Felicity." Of course, thanks to a mid-season premiere promo, it appears as though this version of Laurel may very well be the Black Siren of Earth-2, who was a metahuman and never needed a device to power her sonic scream.

Starring Stephen Amell as the Emerald Archer, “Arrow” airs at 8 pm ET/PT on The CW. The series also stars Emily Bett Rickards, David Ramsey, John Barrowman, Willa Holland and more. “Arrow’s” fifth season returns to the CW on January 25.